In modern digital devices, it is desired to minimize the cost of the device. One way to minimize the cost of a device is to use parts with as loose a tolerance as possible, since the loose tolerance parts tend to be less expensive than their tight tolerance counterparts. However, there are certain portions of a device wherein the loose tolerance of a part may result in poor performance. For example, a clock crystal for use in the generation of a clock signal typically needs to have relatively tight tolerances, especially when the performance of the device depends upon the accuracy of the clock. In a global positioning system (GPS) device, the accuracy of the clock used is critical in determining the position of the GPS device. Therefore, the clock in the GPS device needs to be accurate.
A simple technique involves the use of a clock crystal (or depending upon tolerance requirements, a temperature controlled crystal oscillator) with sufficient accuracy to meet the performance requirement of the device.
Another technique involves the counting of clock ticks of the inaccurate clock for a given amount of time using an accurate clock that already exists in the device and then comparing the results of the count with an expected number of clock ticks and using the difference to adjust the inaccurate clock.
Yet another technique uses software applications to time a count of the clock ticks of the inaccurate clock, then any difference between the count and the expected number of clock ticks can be used to adjust the inaccurate clock.
One disadvantage of the prior art is that the use of a clock crystal with sufficient accuracy can increase the overall cost of the device.
A second disadvantage of the prior art is that the use of a software application to make clock adjustments is that the software application may not be able to execute at a sufficient rate to update the inaccurate clock drift values. This can be a significant problem with inexpensive devices with processors with low processing power, limited by the low cost of the device.